add missing test, oops

Author: Andarist

tests/cases/conformance/controlFlow/controlFlowComputedPropertyNames2.ts

@@ -0,0 +1,17 @@
+// @strict: true
+// @noUncheckedIndexedAccess: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/61389
+
+const arr: number[] = [1, 2, 3];
+const idx: number = 2;
+if (idx in arr) {
+  const x: number = arr[idx]; // ok
+}
+
+const map: Record<string, number> = { a: 1 };
+const key: string = "a";
+if (key in map) {
+  const x: number = map[key]; // ok
+}